14 August 2012

Neurochemical Correlates of Consciousness

A recent post discussed the possibility put forward by Max Velmans that consciousness consists primarily of first-person subjective experience. Consciousness enters “too late” into brain activity to exert any sort of direction or control, Velmans claims. Consciousness can only observe the results of mental activity rather than participating in or initiating it. But now I’ve just finished reading In Search of Memory (2006) by Nobel prize-winning neurobiologist Eric Kandel. It took me awhile to get into this book (recommended, like Velmans’ book, by Lafayette) but eventually I found it enlightening and fairly entertaining. Kandel begs to differ with Velmans: he argues based on neural evidence that there is conscious mental processing, that it is activated by attention, and that it differs from unconscious processing at the level of biochemical action in the neurons. Here are two examples.

1. Forming a Spatial Map of the Environment

By exploring a new environment mice learn to navigate the space with increasing efficiently, quickly moving toward dark enclosures while avoiding brightly lit open spaces. Mice can also learn about their environments by being required to perform a task; e.g., by finding and sitting in the unmarked space that turns off the bright lights and loud noises that mice tend to avoid. To perform this sort of spatial task requires the mouse to pay more attention while investigating the space than when just having a look around the place. It turns out that mice who learn to perform a task retain their memory of the space much longer than do the casual explorers.

Dopamine enhances the response of neurons to stimuli. Dopamine is produced by cells in the mid-brain. The axons of these dopamine-making cells project into the hippocampus, where inputs from various sensory modalities are integrated and stabilized via long-term potentiation of the neural synapses. When the action of dopamine is blocked in the hippocampus of a mouse that learns to perform a spatial task requiring attention, the mouse’s memory of the spatial layout degrades rapidly. Conversely, when the dopamine receptors are activated in the hippocampus of a casually exploring mouse, the mouse retains its memory of the space far longer than would otherwise be expected. The implication is that dopamine stimulates the responsiveness of attention-directing neural pathways in the hippocampus, which in turn trigger the long-term neural retention of spatial layout in memory.

Conversion of short-term to long-term memory requires the activation of genes in the neurons via neurotransmitters that signal the importance of the stimulus for retention. In response to the biochemical signal, the appropriate genes are turned on in the neuron, causing particular proteins to be produced in the cell that are sent to the cell’s synapses, passing along the signal to cells in the hippocampus. In mice, dopamine is the triggering chemical. But the neurochemical memory cascade is triggered differently depending on the type of learning involved. In spatial memory — e.g., mice exploring a new environment — the dopamine activation is initiated from the top down, from the cerebral cortex to the hippocampus. The implication is that the focused attention required for long-term learning — mental activities typically associated with consciousness — follows a neural pathway that’s different from the diffuse mental activity suitable for short-term retention of environmental information.

2. Anxiety

A person who looks at a photo of someone whose facial expression indicates fear shows increased activity in the amygdala, the area of the brain that mediates fear. If the face with the fearful expression is presented for a long period of time, giving the person the opportunity to study the face consciously, then the dorsal region of the amygdala is activated. The dorsal region sends information to the autonomic nervous system, initiating the emotional arousal triggering the fight-or-flight response to frightening stimuli. If on the other hand the face is presented unconsciously — so rapidly that the observer cannot even report what type of expression the face is making — then the basolateral nucleus is activated. This area of the amygdala typically receives sensory input and transmits the signal to the cortex, heightening vigilance toward environmental threats.

Participants in the study were administered a questionnaire assessing their baseline level of anxiety. The level of anxiety had no effect on the conscious reaction to the fearful face. However, baseline anxiety was directly associated with the amount of activation in the basolateral nucleus in the unconscious reaction.

By implication, given the time to evaluate a fear-inducing stimulus consciously, everyone is able to activate the top-down triggering of an appropriate fight-or-flight response. Unconsciously, however, already-anxious people respond to fear-inducing stimuli by becoming hypervigilant, thereby increasing their already-high baseline anxiety levels, whereas non-anxious people do not become more anxious by being presented with a transitory fear-inducing stimulus.

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Thanks very much for your review of this. I’m astounded by the voraciousness of your reading. Seems now I just get through one day’s batch of email newsletters, blogs ( Counterpunch etc), and various detours suggested by them, when the next day’s comes in. I’ve got to get this back in it’s place.

And finish Velmans 2nd edition. Now I’ll have to put the Kandel book further up my to read list – I’m reassured that you found it worthwhile.

I had either to get on with it or to let it drop, since the book is due back at the library tomorrow. Reading Kandel’s reminiscences over a 50-year career you get the sense less of the grand sweep of ideas as of the incremental advances at the scientific frontier. Kandel is a self-professed reductionist — “one cell at a time” is the mantra instilled in him by his mentor. Still, he trained as a psychoanalyst and he studied neural functions in snails based on experimental paradigms of behavioral psychologists. He’s also very high on interdisciplinary collaboration, though for outsiders the separate disciplines he identifies all blur together into hard molecular biology and biochem. In his glimpse into the future at the end of the book he nods toward sociology, especially with respect to mirror neurons. And he does invoke the names of Kant and Locke from time to time, framing the lab work in the larger history of philosophical ideas about mind.

Fascinating. I see implications for teaching here – obviously active learning is supported, and thinking about how to activate attention without derailing into anxiety. I’m putting this into the crop for more digestion.

Right, I agree. From an eliminativist point of view (e.g., Velmans, Metzinger) there would be no reason for you to exhort your students to pay attention, inasmuch as conscious attention is only a consequence of brain-environment activity. Of course I’m presuming that you have on offer something worthy of their attention. But: if intentional attention focuses learning, and learning triggers chemical changes in the neurons, and if chemical changes trigger genetic production of intraneural proteins, and proteins assemble themselves as newly-sprouted synapses linking to the hippocampus, and if intensified neurotransmission across these synapses facilitates long-term memory… This sort of learning cascade is relevant to our prior discussion of intentional causality at your place.

Noamsky piles in on this. I’ve quoted the most relevant section below, from quite a long (and, I find, unusually for Chomsky, irritatingly nebulous) interview from zNet. The interviewer is Peter Hallward, who I guess must be the same PH who wrote ‘Damming the Flood’ about the US overthrow and kidnapping of Aristide in Haiti:

” We can only speculate at the moment, but it’s possible that problems like freedom of the will are mysteries in Hume’s sense, beyond what our cognitive capacities can explain. Of course, there is a question as to whether such freedom even exists, but that’s a rather curious question. William James pointed out, and I think it’s an interesting observation, that the people who argue that freedom of the will doesn’t exist are themselves acting extremely irrationally. Why give us what they take to be reasons? They believe it and are giving these reasons because it’s determined; we don’t believe it because it’s determined. So what’s to discuss?

There’s also a lot of pseudo-scientific argumentation brought in, to try to explain the problem away. For example a couple of years ago there was an interesting discovery, showing that if a person is going to carry out some action, say pick up this pen from a table, there’s activity in the motor cortex of the brain before you’re aware of making the decision.9 This was brought up as an argument against freedom of the will. But it doesn’t tell you anything, except that decisions are made unconsciously, who knows how.

Ph But isn’t one of the cardinal features of free will, at least in the conventional sense, that it’s a matter of voluntary and thus conscious action?

NC It’s a standard assumption that mental acts must somehow be accessible to conscious- ness (‘in principle’). Some philosophers have held that that is a criterion of the mental (notably John Searle, following W.V. Quine). But why take the assumption to be correct (even if it can be formulated coherently, which I doubt, for reasons I’ve discussed) – particularly when there is so much evidence that it is false, for example our best understanding of the mental acts that enter into what you and I are now doing? If we abandon the doctrine – which is just dogma, in my opinion – then it could turn out that there is a distinction between voluntary and conscious. And if that is correct, this experimental work might be evidence for that distinction.

Ph One last question along these lines, before moving on. In the past you’ve said, in passing, that ‘I’m not sure that I want free will to be understood.’10 Is your scepticism about adaptive explanations to the evolution of our ‘instinct for freedom’ purely a response to the unpersuasive science involved, or do you also have normative reasons for rejecting them – perhaps the same sort of reasons at work in your critique of applied behaviourism?

NC To say that the speculations are ‘unpersuasive’ is I think an understatement. Further- more, it is important to distinguish evolutionary accounts from adaptive accounts. It’s well understood in modern biology that these are quite different notions. I wouldn’t quite say that the reasons for the feelings expressed in the statement you quote are ‘normative’. It’s rather that I think that our appreciation of the richness and excitement inspired by human actions would be seriously diminished if it were understood – an eventuality that seems to me remote, despite sophisticated and intriguing work on the topic.

Psychoanalysis

Ph So, if now we admit that, given our current understanding of the biology and psychology, freedom remains an essentially mysterious fact, what then about the domains that border this mystery? There’s been a great deal of work on this sort of problem in the so-called human sciences, over the past century. Psychoanalysis has tried to investigate the boundaries between voluntary and involuntary action, and has explored the ways that people’s formative experiences structure certain aspects of their unconscious life, shaping the more or less repressed desires or drives that account for at least some of their subsequent behaviour. Sociologists have considered the ways that class tends to structure cultural habits or reflexes. Marxists have looked at the ways a given mode of production generates ideological patterns that serve to justify or naturalize the class relations required to sustain it. Someone like your old debating partner Michel Foucault helped to excavate some of the institutional, social and cognitive processes that consolidate norms of behaviour, the ‘biopolitical’ mechanisms that regulate ways of living and reinforce patterns of obedience to the established order of things, ways of governing and being governed. Do you think that this sort of investigation has gone any way towards shedding light on the mysteries of freedom and voluntary action?

NC It’s interesting work but it leaves questions of freedom untouched.

Ph Completely untouched?

NC It shows the influences on our use of freedom. Let’s assume for the moment that we have freedom of will. These studies demonstrate conditions on how we may choose to exer- cise it, but not on its existence in nature. Independently of your class background, cultural influences, and so on, you can still make choices that conflict with them. And many people do, for example dissidents, or revolutionaries, or just independent people.”

I’ll probably take a crack at reading this whole interview later. This from the Chomsky excerpt you posted — “it could turn out that there is a distinction between voluntary and conscious” — is pivotal. Even single-celled organisms act to preserve and perpetuate themselves, but is it voluntary? Doubtful. If humans do have volition, and if most human cognition is unconscious, then the unconscious could be recruited for doing much of the volitional heavy lifting. Traditional psychoanalysis wants to position the unconscious as a repository of the repressed, as if only consciousness exists until repression kicks in. That’s too limiting a role for the unconscious, and establishes an adversarial relation between conscious and unconscious cognition. It’s more likely that, in the absence of internal conflict about desires and preferences, a lot of routine choosing could be accomplished unconsciously, distributedly and quickly, without having to bring online the more resource-intensive and focused decision-making apparatus performed in consciousness.

Hallward is the same guy who writes about Haiti. I’ve read a bit of his stuff: as I recall he’s big on a kind of radical democratic voluntarism predicated on the possibility/necessity of making a decision to resist and to organize, rather than regarding individual volition as being merely a component of neoliberal false-consciousness.

” It’s more likely that, in the absence of internal conflict about desires and preferences, a lot of routine choosing could be accomplished unconsciously, distributedly and quickly, without having to bring online the more resource-intensive and focused decision-making apparatus performed in consciousness.”

Well, obviously that’s how we learn skills – any skill, like typing for instance. But Velmans (and others obviously) seems to be raising the possibility ( I wouldn’t say he advocates anything – he’s too fastidious for that) that we perform our whole lives in the way that we type – without being aware of the decisions we make. Well, to be snobbish, that’s patently true for an awful lot of people, and, to be fair, a lot of them fare much better than me. But more – that our whole lives are like a previously acquired skill, relevantly sort of like Chomsky’s notion of an inherited capacity for language. Everyone can use language, but everyone does something slightly different with it; so too for everything else we do? All the decisions that we think we are making are just like minor adjustments we’d make subconsciously to keep our balance on a bicycle? But no! We still decide what to say or type, or where to go on a bicycle? Almost by definition, it’s hard to say anything sensible about this…

I’m not sure the distinction between voluntary and conscious is so big. Can anything voluntary not be conscious? But better minds than mine…

Anyway, I’m sure this is all still quite tentative speculation, and more experiments will probably change the picture a bit.

Or have we discovered that our lives are pre-programmed like a sort of virtual reality experience, and we’ll come out of it and go – ” wow, that was great; they burned me at the stake!” ? Seems as likely as anything.

‘Voluntarism’ ? I come across this word every so often – usually Marxists dismissing something as ‘voluntarist’. I’ve looked it up a few times, but it seems to have different meanings in so many different feilds that it’s essentially meaningless – which is par for the course for philosophy IMHO. I think philosophy gets an awful lot more reverence than it’s due, though Velmans shows that it can be put to useful purpose sometimes.

I think I heard ( I suppose I could look it up) that Peter Hallward’s background was in religious philosophy or something like that. It seemed strange that it should be him that took it on the job of exposing the knavery around Aristide’s ousting (I refuse to say ouster, though it’s in fashion these days). Same for David Ray Griffin, (the 9/11 books like New Pearl Harbour), who I greatly respect – he was a theologian too. Maybe there’s something in it.

My use of “voluntarism” must have been an unconscious one, since I’m not quite sure what it means either. Presumably it has something to do with deciding rather than just waiting for historical mass movements to pick you up and carry you along into the revolution. I guess Hallward wanted Chomsky to reaffirm the psychological reality of conscious decision-making. At least in the part you excerpted Chomsky isn’t prepared to give Hallward that satisfaction. As you note, Chomsky advocates the “language instinct,” with universal grammar built into the human brain — a position that’s increasingly subjected to critique on both theoretical and empirical grounds. But he’s also famous for acknowledging that humans are capable of spontaneously generating a limitless variety of statements that they had never before heard uttered. So for Chomsky linguistic creativity would fall within the “voluntary unconscious” realm. I was very aware while in France that my use of the French language was much more conscious — I’d plan out what I wanted to say in advance — than when I speak English. Eventually the skill gets compiled and intentional speech becomes more unconscious — like riding a bike. Learning your native tongue doesn’t even seem to require this transition from conscious to unconscious facility. Still, it’s clear enough to me that conscious mediation is crucial in acquiring many new skills in adulthood.

Hallward was at Middlesex when there was a big protest about axing the philosophy department. A lot of academicians signed a complaint sent to the university administrators, with the result being as I recall that grad students were allowed to finish their degrees under advisorship of untenured and lower-paid faculty. Hallward and the other tenured faculty were subsequently hired en masse by some Canadian university. I’ve not followed the trends, but in light of even more draconian austerity measures and rises in tuition fees I would guess that the Middlesex event presaged a lot more downsizing of philosophy and other departments with limited cash value in British universities.